Field of the Invention
An embodiment of the present invention relates to an image forming apparatus including an image forming device that forms an image on paper, a fixing device that fixes the formed image on the paper, a temperature sensor that detects a temperature of the fixing device, and a control unit that switches a position of a conveyance guide in order to switch a conveyance path of the paper. The image forming apparatus includes various kinds of apparatuses such as a copier, printer, a facsimile, and a multifunction printer comprehensively including functions of these.
Description of the Related Art
An electrophotographic image forming apparatus transfers, onto paper, a toner image formed by an image forming device including a photoconductor drum, an exposure device, a developing device, and the like, makes the paper pass through a fixing device including a fixing roller, and fixes the toner image on the paper. The fixing roller is heated with a heating unit such as an electrothermal heater or an induction heater and fixes a toner image on paper by heating and pressing the paper on which the toner image is transferred.
A temperature sensor that detects a temperature of a fixing device, specifically a surface temperature of a fixing roller is provided. Feedback control of the heating unit is performed based on the detection temperature. That is, temperature adjustment control of keeping a surface temperature of the fixing roller at a target temperature is performed. Recently, a contactless thermistor temperature sensor is often used as such a temperature sensor.
Compared to a contact temperature sensor, it is possible to reduce a load on a fixing roller and to increase a life of the fixing roller in the contactless temperature sensor. That is, in a case of the contact temperature sensor, there is a disadvantage that a mark of contact of a temperature sensor is easily left on a surface of a fixing roller. However, there is not such a disadvantage in the contactless temperature sensor. However, generally, the contactless temperature sensor has a weak point that a detection temperature is influenced by surrounding wind and becomes lower than an actual temperature. In order to prevent this, it is necessary, for example, to surround the temperature sensor with a protection against wind.
Furthermore, recently, there is a high demand for a small image forming apparatus that can be provided anywhere. Such a small image forming apparatus is placed in various places including a deskside when being used. Depending on a provided place, there is a case where wind from an air outlet of an air-conditioner or from an electric fan (or circulator) flows into an inner part from a paper ejection opening of an image forming apparatus and a detection temperature in a temperature sensor in a fixing device and temperature adjustment control of a fixing roller are influenced badly.
Specifically, as a result of downsizing of an image forming apparatus, a paper conveyance path from a fixing device to a paper ejection opening becomes short. Thus, even in a contactless temperature sensor surrounded by a protection against wind, there is a case where temperature detection by a temperature sensor is not performed correctly due to an influence of wind flowing from the outside.
On the other hand, in JP 2015-99188 A, an image forming apparatus in which a shutter member, on which opening/closing control is performed, is provided in a paper ejection opening is described. The opening/closing control of the shutter member is performed in order to keep a thermal insulation state of a fixing device. That is, the opening/closing control of the shutter member is performed according to actuation/stoppage of a cooling fan.
It is considered to block wind, which flows from a paper ejection opening of an image forming apparatus into an inner part thereof, by using a shutter member of the image forming apparatus described in JP 2015-99188 A. That is, it is possible to prevent a flow of wind from the paper ejection opening into the inner part by closing the shutter member with a purpose different from a purpose described in JP 2015-99188 A, that is, with a purpose of preventing failure in correct temperature detection, which is performed by a temperature sensor, due to wind flowing from the outside. However, in this case, a shutter member and a mechanism that opens/closes that become necessary and a cost of the image forming apparatus is increased.
On the other hand, there are many image forming apparatuses that can perform duplex printing. In those image forming apparatuses, a path switching gate that can switch conveyance of paper after single-sided printing to a reverse conveyance path and conveyance of paper after duplex printing to a paper ejection opening is included in a conveyance path of paper. Alternatively, there is an image forming apparatus which includes a sheet postprocessing device to bundle a plurality of pieces of paper elected from a paper ejection opening and to perform postprocessing such as stapling processing and in which a lowered position and an elevated position of a postprocessing tray are switched.